Hairy Roots as a Source of Tropane Alkaloids

The hairy roots developed after Agrobacterium rhizogenes transformation can be used for the production of secondary metabolites which show medicinal properties. Plant secondary metabolites include various classes of chemical compounds, such as the tropane alkaloids found in some members of the Solanaceae family, for example, Atropa belladonna, Datura stramonium, D. innoxia, Hyoscyamus muticus, and H. niger. This chapter presents the strategy for producing tropane alkaloids such as scopolamine and hyoscyamine by the hairy roots of these species. High biomass production of D. stramonium and D. innoxia hairy roots and the associated bioactive compounds can be enabled by optimization of the medium. In addition, scopolamine and hyoscyamine production can be enhanced by optimizing various culture conditions, such as the type of the medium or sucrose concentration, and the ploidy level of H. muticus hairy roots. Their production by A. belladonna hairy roots can also be influenced by the ammonium or nitrate concentration of the medium. Tropane alkaloid production by hairy roots can be significantly increased by the use of elicitor treatments such as chitosan, acetic acid, citric acid, jasmonic acid, acetylsalicylic acid, or aluminum chloride: for example, treatment with Tween 20, combined with L-phenylalanine or DL-s-phenyllactic acid alone or with tropinone feeding, increased the level of hyoscyamine released into the medium by D. innoxia hairy roots. Secondary metabolite production can also be improved by transgenic manipulation: tropane alkaloid biosynthesis can be raised by overexpression of the genes encoding the enzymes involved in the tropane alkaloid biosynthesis pathway such as hyoscyamine-6s-hydroxylase (H6H), putrescine N-methyltransferase (PMT), or tropinone reductase I and II (TR I and TR II). Alkaloid production can be influenced by overexpression of genes encoding enzymes involved in the tropane alkaloid biosynthesis pathway, as well as by genetic manipulation based on gene silencing. The cultivation of D. innoxia and H. niger hairy roots in bubbling bioreactors may also serve as an efficient culture for large-scale tropane alkaloid production.